Electrochemical Analysis of Mechanically Flexible Magnesiumion Battery Electrodes in a Polymer Gel Perchlorate Electrolyte

Abstract

Over the past decade, rechargeable batteries based on lithium metal ion chemistries have enabled the practical development of many new products and technologies. Today, Li-ion batteries are often the primary means of providing electrical power to a diverse and growing number of devices, from mobile phones to electric vehicles. Despite many advances, Li-ion battery technologies suffer from some limitations that can prevent their use in emerging market sectors such as wearables, IoT, and grid-scale energy storage. While still in the research and development phase, it is anticipated that divalent metal-ion battery chemistries based on zinc or magnesium will present viable alternatives to conventional lithium-ion cells in these markets. Lithium ion batteries have a high theoretical gravimetric capacity of 3829mAh/g but only a modest volumetric capacity of 2044mAh/cm3. By comparison, divalent batteries based on zinc or magnesium ions have theoretical volumetric capacities of 5854mAh/cm3 and 3882mAh/cm3 respectively. Volumetric capacity is especially important in IoT devices and wearables, where thin, flexible batteries which can cover large areas are ideal. In addition to a somewhat low volumetric capacity, lithium is far less common in the earth's crust than magnesium or zinc and possesses higher reactivity. Because of this, lithium-ion batteries are anticipated to be less environmentally friendly and cost effective than divalent metal-ion batteries in applications requiring many large battery cells. In this proceeding, we study the components of an experimental magnesium ion half-cell constructed from solid, flexible materials. A magnesium-ion cell was chosen due to its low material cost, good theoretical volumetric capacity, simple fabrication steps, and separator-free reaction chemistry. Flexible, insertion-type anodes and cathodes were fabricated using bismuth nanotubes and tungsten disulfide respectively. A polymer-based electrolyte made of PVDF-HFP and magnesium perchlorate was chosen for its demonstrated high ionic conductivity and mechanical flexibility. Each interface of the half-cell was characterized though the use of cyclic voltammetry. Cell fabrication, component/interface electrochemistry, electrode materials and packaging, will be described in detail.